For trouble-free operation of an elevator, it is necessary that the elevator should run along a vertical line. The elevator is normally installed in an elevator shaft built from concrete. The guide rails for the elevator car and counter-weight are fixed to the shaft walls using rail fixtures. During the installation of the elevator, the guide rails and other shaft equipment are adjusted to their proper positions. In this context, shaft equipment refers to guide rails, landing doors and their mounting brackets. In the vertical direction, the alignment is effected using plumb lines, which are fixed at a point above the shaft equipment to be installed in the elevator shaft and which extend through the whole length of the shaft. It has also been suggested that the alignment could be done using a laser beam, but this method has not gained ground due to the costs and the difficult conditions at the site of the installation.
In prior art, the plumb lines are fixed to the floor of a machine room above the shaft and so positioned that they can be used to align the shaft equipment, such as guide rails, and the landing doors. The ceiling of the elevator shaft must be provided with holes for the plumb lines.